Field of the Invention
The invention relates to a stable, highly concentrated, aqueous suspension of nanoparticles, particularly of titanium dioxide particles, a method for production, and use of the suspension, e.g. for coating or impregnation, or as an additive in organic or inorganic matrices.
Description of Related Art
As nanoadditives, nanoparticles (particle size typically <100 nm) possess great potential for innovation, e.g. in coatings, plastics, optical articles, electronics, ceramics, specialty chemicals, etc. The nanoparticles can have different functions in this context, e.g. as photocatalysts, UV absorbers, abrasion protection, fillers, or for surface functionalization.
Owing to the small particle size and the strong tendency to agglomerate, it is usually not possible to process and apply nanoparticles in dry, powder state. For this reason, water- or solvent-based dispersions (suspensions) of the nanoparticles are produced as an alternative, various technologies being used to disagglomerate and disperse the particles. It is, however, of decisive importance that a very good, stable state of dispersion is achieved in order to be able to exploit the advantage of nanoadditives over the familiar microparticulate additives in use. If the nanoparticulate suspension is applied to a substrate as a coating, for example, the transparency of the suspension plays an important role.
Numerous methods have already been developed for effective dispersion of nanoparticles in various dispersion media, such as mixing with a high shear rate, ultrasonic treatment or various grinding technologies. In addition, various dispersants and other additives are known that can advantageously be used in a nanoparticulate suspension.
DE 10 2004 037 118 A1, for example, discloses a method for manufacturing an aqueous suspension of nanoscale titanium dioxide particles with a concentration of at least 20% by weight, where an amino alcohol and a carboxylic acid are used as dispersants and grinding is performed in a high-energy mill following predispersion.
According to WO 2010/110726 A1, amines or glycols are used as dispersants, and the suspension is ground in a bead mill with grinding media of a specified size.
In the known methods, a marked increase in viscosity often occurs during or after dispersion with high shear rates, e.g. in an attrition mill, this making further processing more difficult.